Carbon nano tubes are known for their conductive or semiconductive properties due to the elongated tubulous structure. They are used especially in the field of industrial technology. The plurality of industrial applications of CNTs shows the need for improving the production process to obtain higher specific quality at increased quantities.
A number of methods synthesising vertically aligned CNTs are known from prior art. The majority of synthesis comprise a formation of a catalyst layer on which CNTs are developed. Popular methods obtaining such catalyst layer are sputtering, deposition processes, such as electron beam deposition, thermal deposition and the like. Preferred processes for growing CNT thereon include arc discharge, laser vaporisation, gas phase synthesis, CVD (Chemical vapor deposition) method, which include thermal CVD method, plasma CVD and the like.
Recent ambitions show that CNTs are developed on defined local areas on the catalyst layer to obtain vertically aligned nano tubes, by reasons of which a formation of such local areas has to be performed prior to the development of the carbon nano tubes.
The EP 1 059 266 A1 describes a method of synthesising carbon nano tubes where a catalyst layer comprising the catalytic metal particles is obtained by thermal deposition, sputtering or electron beam deposition. Local isolated catalytic metal particles from the metal catalyst layer are subsequently formed by etching the catalyst layer. Another possibility for obtaining isolated particles is the use of photolithography. Thereby, the catalyst layer is coated with photoresist and subjected to exposure and development processing to form a nanosized photoresist pattern which is used as an etching mask to form the isolated catalytic particles. The size and the density of particles can be controlled by controlling the size and density of the photoresist pattern. Growing the nano tubes is performed by thermal chemical vapor deposition in which a carbon source gas is supplied to a thermal CVD apparatus to form carbon nano tubes.
When electron beam deposition is used for obtaining a catalyst layer the actual deposition does not take place on the support member on which the electrons are impacting. The electron beams are used to evaporate particles from the surface of metal catalyst which are then deposited as catalytically active particles on the support member. The formation of a catalyst layer can not be performed directly on the support member.
Preparing an existing catalyst layer by the use of electron beams, in particular in relation to photolithographical methods, especially the exposure, results in high impact depths on the surface of the catalyst layer. This does not often give a favourable result because the impact of electrons might easily damage the catalyst and additional procedural steps are necessary. This clearly is a significant economic disadvantage when mass production is required.
Etching methods which are preferably used in industrial mass production in the field of nano technology are time consuming processes since a number of procedural steps are needed for the preparation of a catalyst layer. Furthermore, additional substances and/or materials are required in order to perform such preparations. This can easily cause detriments to the catalytic particles and a proper synthesis of a CNT subsequent to the preparation of a catalyst layer is not satisfying. It might even result in hindering the entire process of synthesising CNTs. These factors, in particular the time consuming and cost factor, play an important role in industrial production.
Therefore, it is an object of the present invention to provide an improved method of synthesising carbon nano tubes which limits or avoids the above mentioned problems and simplifies the entire process. A main object of the present invention is to gain the controlled synthesis of CNT by reducing and even omitting procedural, i.e. preparatory steps. Moreover, it is an object of the present invention to obtain a method which provides the control and the influence of the CNT during and/or after the synthesis without additional means or apparatuses.